A typical roller cone earth-boring bit has a bit body with three bit legs. A bearing pin extends from each bit leg, and a cone rotatably mounts on the bearing pin. The bearing surfaces between the cavity of the cone and the bearing pin are filled with lubricant. A seal is located between the cone and the bearing pin to seal lubricant within and keep drilling fluid from entering.
During operation, a high downward force is imposed on the drill bit from the weight of the drill string. The downward force transmits through the bit body and bearing pin to the cone. Even though the clearances between the bearing surfaces are quite small, slight misalignment of the cone bearing surface with the bearing pin tends to occur. This slight misalignment can result in uneven contact stress.
The seal between the cone and the bearing pin for sealing lubricant is also affected by the load imposed on the bit. Typically, the contact pressure will be greater on the lower side of the seal than on the upper side. Varying seal contact pressure can be caused by misalignment of the cone bearing surface and bearing pin. Changes in contact pressure can cause excessive heat in certain areas of the seal, shortening the life.